With regard to a magnetic head for a hard disc device, recently, for use with an inductive head at writing side, a complex magnetic head (herein after will be called as complex head) in which such as an MR head, GMR head and TMR head (herein after will be represented as MR head) is used at a read out side.
Recording density of a hard disc is steadily increasing such as to a few ten gigabyte/inch. In addition, installations of an HDD to home electric appliances with digital technologies accelerate the density increase. For this reason, a demand for magnetic head assemblies, which are indispensable for the installation of the HDD, is increasing rapidly.
The magnetic head assembly is usually constituted by such as a head slider, which installs a complex head having an MR head and a suspension spring for supporting the same, the head slider is fixed to a head actuator such as a voice coil motor via the suspension spring.
The complex head in the head slider is formed integrally with the slider through a thin film process. Different from the inductive head at a write side, in the MR head defects such as resistance defect, insulation defect between shields and electric characteristic defect are likely caused. Therefore, an electrical characteristic testing of the magnetic heads including such as MR heads is performed under a condition of slider single body.
For a defect testing of a head slider (slider single body condition) prior to assembling into a head assembly, a testing apparatus, which measures a reproducing characteristic of an MR head by applying externally a DC magnetic field to the MR head is disclosed and known from JP2000-260012A.
Further, for testing under assembled condition as a head assembly, a testing of an MR head in which while applying such as an AC recording magnetic field to the MR head and applying externally a DC magnetic field thereto, an output voltage waveform is obtained from the MR head to determine the characteristic is disclosed and known from JPH10-124828A.
The size of a head slider is at most 1 mm square or less and on the side face at the trailing edge of the head slider four or six connection terminals for a complex head are provided. The height of the head slider is about 0.5 mm, and usually the magnetic head is also provided at the trailing edge of the head slider together with the connection terminals. During testing of the head slider (under slider single body condition), if the connection terminals of four or six are not surely contacted with a probe, the testing cannot be performed successfully.
Moreover, when measuring a reproducing characteristic of an MR head under a condition of applying a DC magnetic field externally, in these sorts of testing apparatus, an external magnetic field generating device has to be disposed extremely close to the head slider. Further, the measurement items have to cover a wide range of testing such as quasi-magnetic response characteristic test (QUASI-TEST) of the MR head and hysteresis characteristic test as a magnetic material, and in addition, the testing has to be completed in a short time (about one second) for one piece of head slider.
An MR head is an element, which varies its resistivity in response to the magnetic field generated from data recorded on a medium. Therefore the quasi-magnetic response characteristic test is not a test in which the MR head reads data actually written on a magnetic disc, but a test for determining a reading characteristic in which a like high frequency magnetic field as a written data is applied externally in a quasi manner to the MR head so as to constitute a circumstance as if the MR head received the magnetic field when data are read. This test requires repeating measurement under a same condition about a few hundreds of times. Moreover, the test is required to vary the magnitude and direction of the magnetic field intensity to be applied to the MR head. Namely, an external magnetic field generating device generating a high frequency magnetic field is required which alternates of the magnetic field from 0 to + side of a predetermined level (for example, magnetic field directing downward with respect to the head slider) and then from 0 to − side of a predetermined level (for example, magnetic field directing upward with respect to the head slider).
On the other hand, the hysteresis characteristic test is performed in such a manner that a DC magnetic field is applied externally, while increasing successively the magnetic field intensity (magnitude of the magnetic field) from 0 to + side and then decreasing to return to 0, subsequently the magnetic field intensity of side is increased and the decreased to return to 0. For this reason, it is necessary to generate a DC magnetic field of large intensity. Therefore, provision of another separate external magnetic field generating device is required.
These two separate external magnetic field generating devices require respectively such as a power source and a current output circuit. However, since the test area where the connection terminals of the head slider contact with the probe is limited to one portion, only a single core having an air gap in which magnetic field is generated can be provided therein. For this reason, in these sorts of test apparatus, a fine wire for a high frequency magnetic field generation coil and a thick wire for a DC magnetic field generation coil are wound on the single core. The magnetic field generation efficiency of these coils reduces as the position thereof on the core is separated from the test area. Therefore, if the inductance thereof is not increased, a magnetic field having a desired intensity cannot be generated at the test area (air gap). If the inductance is increased, a leakage magnetic field to the surroundings increases.
When a rectangular frame shaped core is used, in these sorts of magnetic head slider test apparatus, it is difficult to provide two series of coils for the DC magnetic field generation and for the high frequency magnetic field generation on one side having the air gap because of the layout such as of a test stage and test probe provided around the test area. For this reason, the coils have to be provided on the back side opposing to the side having the test area (air gap) as disclosed in FIG. 1 of JPH10-124828A. In this instance, since the position of the coils are remote from the air gap (test area), the inductance (number of their turns) of the coils increases, and an increase of the leakage magnetic field to the surroundings cannot be avoided, which adversely affects the test result and in addition causes a problem of increasing the entire size of the apparatus.